Take-home message: Femtosecond lasers differ in their indications, energy delivery parameters, and hardware features. Understanding the implications of these factors will enable an objective assessment of the available technology.
Cleveland—Understanding how hardware design and technical specifications affect femtosecond laser performance provides surgeons with the fundamental knowledge they need to evaluate the available systems and choose one that will best fit their needs, according to Ronald R. Krueger, MD, MSE.
Dr. Krueger discussed the implications of different laser parameters and provided an overview of the features of commercially available femtosecond laser platforms. The latter are represented by systems used for cornea/refractive applications only (IntraLase, Abbott Medical Optics; FS200, Alcon Laboratories, Femto LDV Z4 and Z6; Ziemer; VisuMax, Carl Zeiss Meditec), cataract surgery only (LENSAR, LENSAR; Catalys, Abbott Medical Optics), and units that can be used for both cornea/refractive and cataract procedures (LenSx, Alcon; Femto LDV Z8, Ziemer; Victus, Technolas). (Note: approved indications for each laser vary by country.)
“At the present time, the best lasers for refractive procedures are those with refractive-only optics and design, while the best lasers for cataract surgery have cataract-only optics and design,” said Dr. Krueger, medical director, Department of Refractive Surgery, Cole Eye Institute, Cleveland Clinic, Cleveland, OH.
“This is important to consider, as providers who seek both a refractive and cataract laser might be tempted to get one for both indications,” he said.
Factors affecting energy delivery with femtosecond lasers include pulse duration, numerical aperture, and wavelength. When it comes to pulse duration and wavelength, shorter is better, as both require less energy density for photodisruption.
Currently, surgeons do not have options when it comes to laser wavelength since all femtosecond lasers use a near infrared wavelength.
However, ultraviolet units, which would significantly reduce the energy density needed for photodisruption, may be available in the future, Dr. Krueger said.
In terms of numerical aperture, larger is preferable, as it provides a tighter focus and thereby enables the use of lower energy.
Pulse frequency (repetition rate) and pulse separation are other important variables in the performance of femtosecond lasers. A higher pulse frequency may allow for a shorter procedure time and/or a shortening of pulse separation distance. The latter is important for achieving the desired tissue effect with lower energies, which helps to minimize collateral tissue damage and procedural side effects.